The present invention relates to a hearing aid which is adapted to be received at least almost fully in an auditory canal of a user in at least locally fitting manner, comprising a device housing having on a proximal side a microphone, a loudspeaker which via at least one transmission channel is in open communication with a sound-emitting opening of the device, a battery chamber for receiving a battery therein, and comprising a sound processing device for generating sound received by the microphone to the loudspeaker in at least partly processed manner.
Such a hearing aid is for instance known from International patent application WO 01/41503. The hearing aid described herein comprises two parts of a device housing releasably connected to each other and is provided on a proximal side with a microphone. The device further comprises a loudspeaker for generating the sound received by the microphone, after it has been amplified and/or processed by the sound processing device, to a sound-emitting opening situated on a distal outer end of the device. The two device parts enclose a cavity which forms, distally of the loudspeaker, both a transmission channel between the loudspeaker and the sound-emitting opening and a battery chamber. The battery chamber provides space for a battery which electrically powers the device during operation. An outer shell of the two parts is herein shaped to the size of the individual anatomy of the auditory canal of the user and fits closely therein. This hearing aid is particularly intended for placing deep inside the auditory canal so that no parts thereof protrude or are visible outside the ear.
Partially due to the relatively short distance in such a hearing aid between the proximal side with the microphone on the one hand and the distal end with the sound-emitting opening on the other, there is a very real danger of so-called acoustic feedback. Sound generated by the loudspeaker via the sound-emitting opening is here picked up by the microphone and then, amplified or processed, once again generated via the loudspeaker and picked up again by the microphone, and so on, this eventually resulting in an extremely irritating whistle or screeching tone drowning everything out. It goes without saying that such feedback is highly irritating to the user.